#include<iostream.h>
#include<math.h>
class point{
public:
	double x;
	double y;
	point();
	point(double a,double b);
};
point::point()
{
	x=0;
	y=0;
}
point::point(double a,double b)
{
	x=a;
	y=b;
}
class line{
private:
	point M;
	point N;
	double length;
public:
	line();
	line(point A,point B);
	void print();
};
line::line()
{
	length=0;
}
line::line(point A,point B)
{
	length=sqrt((A.x-B.x)*(A.x-B.x)+(A.y-B.y)*(A.y-B.y));
}
void line::print()
{
	cout<<"線的長度"<<length<<endl;
}
void main()
{
	point a;
	cout<<"輸入點a的橫坐標:";
	cin>>a.x;
	cout<<"輸入點a的縱坐標:";
	cin>>a.y;
	point b;
	cout<<"輸入點b的橫坐標:";
	cin>>b.x;
	cout<<"輸入點b的縱坐標:";
	cin>>b.y;
	line L(a,b);

	L.print();
}